J . Am. Chem. SOC.1988, 110, 4451-4453
Interaction of VCl,(thf), with excess NaBH, in I ,2-dimethoxyethane (dme) gives a purple solution: from which the first binary tetrahydroborate of vanadium, [Na(dme)] [V(BH,),], 1,I0 may be obtained after crystallization from diethyl ether (see Scheme I). The infrared spectrum of 1 is consistent with an eight-coVCl,(thf), + 4NaBH4 dme [Na(dme)][V(BH,),] + 3NaCI 3thf
+
-
+
ordinate geometry in which the vanadium center is surrounded by four bidentate BH4- groups. Treatment of [V(BH,);] solutions with PMe,, or more conveniently, interaction of VCI3(PMeJ2 with LiBH,, yields the neutral tris(tetrahydroborate), V(BH,),(PMe,),, 2.'l This bright green paramagnetic complex (pUeff = 2.5 re) possesses three strong IR bands in a pattern characteristic of bidentate BH4- groups. VCI,(PMe3), + 3LiBH4 V(BH4),(PMe3), 3LiC1
-
+
The X-ray crystal structure of 2 (Figure la)', reveals a nearly ideal D3,,hexagonal bipyramid with three bidentate BH4- groups in the equatorial plane and two PMe li ands occupying the axial sites. The V-P distance of 2.5 10 (1 Agis comparable with those of other vanadium phosphine complexes, while the V-H and V.-B distances of 1.83 (3) A and 2.365 (5) A, respectively, are similar to those in other vanadium BH,-complexes.' This structure differs fundamentally from that of the d' titanium analogue Ti(BH,)3(PMe,),,', in which the symmetry is lowered to C, and two of the tetrahydroborate groups adopt unusual "side-on" bonding geometries. The structural differences between the titanium and vanadium species may arise from a Jahn-Teller distortion: in D3,, symmetry, the electronic configuration is orbitally degenerate (Jahn-Teller susceptible) for a dl ion but orbitally nondegenerate for a d2 ion. Treatment of V(BH,),(PMe3), with excess 1,2-bis(dimethylphosphino)ethane (dmpe), gives dmpe-BH, and a purple vanadium(I1) product V(BH,),(dmpe),, 3.14 This species, which may VCl,(dmpe), + 2NaBH4 V(BH,),(dmpe), 2NaC1
f
-
+
also be prepared from VClz(dmpe)2and NaBH, in tetrahydrofuran, is paramagnetic (ref[= 3 . 6 ~ and ~ ) possesses two strong broad vBH IR bands of equal intensity and an intense absorption at 1060 cm-I that has been attributed to unidentate BH,- coordination.Ia The X-ray crystal structure (Figure 1b)lSreveals that both tetrahydroborate groups are indeed unidentate. The vanadium center adopts a trans octahedral geometry with V-P = 2.503 (1) A, V-H = 1.88 (3) A, and V-B = 2.833 (4) A. The V-H (7) (a) Marks, T. J.; Kennelly, W. J. J . Am. Chem. SOC. 1975, 97, 1439-1443. (b) Kinney, R. J.; Jones, W. D.; Bergman, R. G.J . A m . Chem. SOC.1978,100,7902-7915. (c) Cotton. F. A.; Duraj, S. A,; Roth, W. J. Inorg. Chem. 1984, 23,4113-4115. (d) Cotton, F. A.; Duraj, S. A.; Falvello, L. R.; Roth, W. J. Inorg. Chem. 1985, 24, 4389-4393. (e) Hessen, B.; Teuben, J. H.; Lemmen, T. H.; Huffman, J. C.; Caulton, K. G.Organometallics 1985, 4, 946-948. (8) *V(BH4)3*has teen claimed, but no data have been reported. Klejnot, 0. Dissertation, University of Munich, 1955. (9) Makhaev, V. D.; Semenenko, K. N. Bull. Acad. Sci. USSR 1978,27, 2520-2521. (IO) IR (Nujol, cm-') 2462 s, 2396 s, 2296 m, 2214 m, 2069 s, 1959 m. Anal. Calcd: C, 21.5; H, 11.7; V, 22.8. Found: C, 22.2; H, 10.7; V, 21.4. ( I I ) IR (Nujol, cm-') 2431 s, 2385 s, 2227 w, 2218 w, 2087 s, 1951 w; 'H N M R (C6D6, 25 " c ) S -12.4 (s, fwhm = 300 Hz, PMe,). Anal. Calcd: C, 29.1; H, 12.2; V, 20.6. Found: C, 28.6; H, 12.3; V, 20.3. (12) Spacegrou ( 50 "C) Pnma, with a = 10.350 ( I ) A, b = 11.095 (2) A, c = 14.228 (2) =; 1634 ( I ) A', Z = 4, RF = 3.4%. R,F = 2.9% on 128 variables and 959 data with I > 2.58a(I). Atoms V, PI, P2, C1, C3, BI, H l a , H3a, H11, and HI2 were constrained to the crystallographic mirror plane at y = 0.25, all non-hydrogen atoms were refined anisotropically, and the hydrogen atoms were located in the difference Fourier maps and refined with independent isotropic thermal parameters. (13) Jensen, J. A.; Girolami, G. S. J . Chem. Soc., Chem. Commun. 1986, 1160-1 162. (14) IR (Nujol, cm-') 2341 sh, 2312 vs b, 2110 sh, 2095 vs b; 'HNMR (C&, 25 " c ) 6 -8.6 (s, fwhm = 500 Hz, PCH,), -19.3 (s, fwhm = 950 Hz, PMe,). Anal. Calcd: C, 37.8; H, 10.6; V, 13.4. Found: C, 37.8; H, 10.4; V, 13.5. (15) Space group (-75 "C) P 2 , / n , with a = 8.469 (2) A, b = 13.735 (4) A,c=9.666(7)A,8=96.14(3)";V= lll8(2)A3,Z=2,RF-3.2%,RwF = 3.0% on 168 variables and 1629 data with I > 2.58a(I). Non-hydrogen atoms and hydrogen atoms were refined as above.
i,
0002-7863/88/1510-4451$01.50/0
445 1
distance is comparable to that in 2, but the long V-B distance clearly establishes the q 1 bonding mode. The V-H-B angle of 140 (1)O is intermediate between those of 121.7 (4)O for Cu(q1-BH4)(PMePh,)3and 161.7' for FeH(q'-BH,)(dmpe),.l4 The structure of 3 again differs from that of its titanium analogue, Ti(BH,),(dmpe),, which possesses an eight-coordinate geometry with bidentate BH4- ligands.16 The difference may be attributed to the smaller size of vanadium and to the preference of d3 species to adopt octahedral coordination environments. Interestingly, despite the q1-BH4coordination, 3 does nor react with Lewis bases such as PMe, and excess dmpe. These vanadium complexes are of interest as molecules that contain V-H bonds;I7 further, 3 is notable as the first example of a crystallographically characterized bis(q'-BH,) complex. Vanadium tetrahydroborates may also prove useful as molecular precursors for ceramic thin films, as shown by the formation of TiB, by thermolysis of the titanium tris(tetrahydrob0rate) Ti(BH4),(dme).I8 Further studies along these directions are in progress.
Acknowledgment. We thank the National Science Foundation (Grant C H E 85-21757) and the Office of Naval Research under their Young Investigator Award Program for support of this research. We particularly acknowledge Dr. Scott Wilson and Charlotte Stern of the University of Illinois X-ray Crystallographic Laboratory for performing the X-ray crystal structure determination. G.S.G. is the recipient of an A. P. Sloan Foundation Fellowship (1988-1990). Supplementary Material Available: Tables of atomic coordinates and complete lists of bond distances and angles for V(BH,),(PMe,), and V(BH,),(dmpe), (4 pages); tables of observed and calculated structure factors for V(BH4),(PMe,), and V(BH,),(dmpe), (1 1 pages). Ordering information is given on any current masthead page. (16) Jensen, J. A.; Wilson, S.R.; Schultz, A. J.; Girolami, G. S. J . Am. Chem. Soc. 1987, 109, 8094-8096. (17) Hessen, B.; Van Bolhuis, F.; Teuben, J. H. J . Am. Chem. SOC.1988, 110, 295-296. (18) Jensen, J. A.; Gozum, J. E.; Pollina, D. M.; Girolami, G . S. J . Am. Chem. SOC.1988, 110, 1643-1644.
Evidence for Centrally Directed Bonds in Trinuclear Metal Cluster Compounds: The Apparent Free Rotation of the Cr(CO)S Unit in (OC)sCr[Os(CO)3(PMe3)]2 Harry B. Davis, Frederick W. B. Einstein, Victor J. Johnston, and Roland K. Pomeroy* Department of Chemistry, Simon Fraser University Burnaby, British Columbia, Canada V5A 1S6 Received January 25. 1988 Metal-metal bonds in trinuclear clusters are usually regarded as two-center two-electron bonds.' There are, however, studies that indicate that the metal-metal bonding in these compounds should be described in terms of a centrally directed, three-center two-electron molecular orbital, along with edge-bridging molecular orbitals.2 We have recently reported observations consistent with the latter view for O S ~ ( C O ) ~Here ~ . ~we present evidence that in solution the Cr(CO)5 unit freely rotates in both isomers of the ( 1 ) For example: (a) Cotton, F. A,; Wilkinson, G.Advanced Inorganic Chemisfry, 4th ed.; Wiley: New York, 1980; p 1083. (b) Wade, K. In TramifionMeral Clusrers;Johnson, B. F. G., Ed.; Wiley: Chicester, England, 1980; p 211. (2) (a) Delley, B.; Manning, M. C.; Ellis, D. E.; Berkowitz, J.; Trogler, W. C. Inorg. Chem. 1982, 21, 2247 and references therein. (b) Lauher, J. W. J . Am. Chem. SOC.1982, 100, 5305. See, also: Porterfield, W. W. Inorganic Chemistry; Addison-Wesley: Reading, MA, 1984; p 551, (3) Johnston, V. J.; Einstein, F. W. B.; Pomeroy, R. K. J . Am. Chem. SOC. 1987, 109, 8111.
0 1988 American Chemical Society
Communications to the Editor
4452 J . Am. Chem. SOC.,Vol. 110, No. 13, 1988
parallel (equatorial) to the M3 plane.' However, and as can be seen from Figure 1, the radial carbonyls of the Cr(CO), group are considerably rotated from this arrangement, e.g., the dihedral angle between the Os( l)-Os(2)-Cr and C0(31)-Cr-C0(34) planes is 25.5 (2)'. This staggered arrangement is more typical of bimetallic (L)(OC),MM'(CO),(L) complexes where there is free rotation about the metal-metal single b ~ n d . ~ , ' ~ The I3C N M R spectrum of 1 (I3CO-enriched) in CHFCI,/ CD2CI2at -122 "C (Figure 2) is consistent with the presence of roughly equal concentrations of two isomers, A and B as shown (Me and axial C O groups have been omitted). The assignment 0
0 CQ
Ca
Figure 1. Molecular structure of ( O C ) , C ~ [ O S ( C O ) , ( P M ~ , )(1). ]~
c
c
0'
0 A
230
220
210
200
190
180
ppm
Figure 2. 100.6-MHz I3C N M R spectrum of 1 ("CO-enriched) in CHFC12/CD2C12 solution at -122 OC. The assignment of the signals is as shown in the text except that signals labeled d, f, and i refer to the axial carbonyls on the osmium atoms labeled d, f, and i in the text.
trinuclear cluster (OC),Cr[Os(CO),(PMe,)] 2. This suggests that the only bond between the chromium atom and the two osmium atoms is a centrally directed, three-center two-electron bond. The cluster (0C),Cr[OS(CO),(PMe3)1, (1) was isolated as deep red, air-stable crystals from the UV irradiation of (Me,P)( O C ) , O S C ~ ( C O )in~ ~C6F6., The structure6 of 1 (Figure 1) consists of a triangular CrOs, unit with Cr-Os vectors of 3.024 (2) A (Os( l)-Cr) and 2.996 (2) 8, (Os(Z)-Cr) and an Os+ bond of length 2.838 (1) A. There do not appear to be any Cr-Os bond lengths reported in the literature. The Cr-Os lengths in 1 are, however, slightly longer than 2.979 (1) A, the length of the dative Os-Cr bond in (M~,P)(OC),OSC~(CO),.~ Dative metal-metal bonds are usually longer than comparable covalent metal-metal bonds8 The carbonyls of M(CO), units in trinuclear clusters usually occupy sites that are either essentially perpendicular (axial) or (4) Prepared in a similar manner to (Me,P)(OC),OsW(CO),: Einstein, F. W. B.; Jones, T.; Pomeroy, R. K.; Rushman, P. J . Am. Chem. SOC.1984, 106. 2707. (5) Isolated yield: 31% (after chromatography). IR v ( C 0 ) (hexane) 2074 (w), 2003 (s), 1991 (vs), 1955 (w), 1939 (m), 1920 (w), 1887 (w, br) cm"; MS, m / e 892 (M'); "C N M R (CHFCI2/CD2Cl4,4/1, -122 "C) 8 232.0, 223.3, 221.2, 202.1, 201.2, 199.7, 180.7, 179.2 177.4. anal. calcd for C17Hi8CrOs20,1P2: C, 22.87; H, 2.03. Found: C, 23.09; H , 2.04. (6).X-ray diffraction data for (OC)#3[Os(C0)3(PMe l 2 M , = 892.4: c = 12.357 (1) triclinic; space groupP1; u = 9.331 (1) A, b = 12.013 (1) A, a = 87.35 (l)', P = 85.94 (l)', y = 68.81 (l)', V = 1287.9 A), 2 = 2, D, = 2.302 g cm-' (an analytical absorption correction was applied); diffractometer, Enraf-Nonius CAD4F; radiation, Mo Ka, graphite monochromator ( X ( K a , ) = 0.709 30 A); scan range = 0" 5 2 8 5 50°; reflections = 3660 with I, 2 2.5a10; (number of variables = 213) Rr = 0.0406, R, = 0.0501. (7) Davis, H. B.; Einstein, F. W. B.; Glavina, P. G.; Jones, T.; Pomeroy, R. K.; Rushman, P., to be submitted for publication. (8) Einstein, F. W. B.; Jennings, M. C.; Krentz, R.; Pomeroy, R. K.; Rushman, P.; Willis, A. C. Inorg. Chem. 1987, 26, 1341.
d.
B
shown is straightforward based on the characteristic region the resonances of carbonyls of a given type occur,ii the intensities, and the mode of collapse of the signals at higher temperature (when a given mechanism is assumed). As can be seen, even at -122 'C the four radial carbonyls of the Cr(CO), unit in each isomer are equivalent but not equivalent to the fifth (axiali2) carbonyl. For A, this equivalence cannot be due to the radial carbonyls adopting positions an equal distance above and below the CrOs2 plane because the osmium atoms are chemically different (Figure 1 ) . Accidental degeneracy can also be confidently ruled out; for trinuclear clusters, there is usually a large chemical shift difference between carbonyls located in the metal plane and those perpendicular to the plane." Furthermore, we have observed similar equivalence of carbonyls in compounds related to 1 including (OC),W [Os(CO),( PMe,)] and [ (Me0)3P](OC), W [ O S ( C O ) ~ ( P M ~ , ) ] We ~ . ' ~believe the simplest explanation for this observation is that the Cr(CO), unit in each isomer of 1 freely rotates in much the same way as in binuclear complexes with unbridged, single metal-metal bonds. This implies that the bond between the chromium atom and the two osmium atoms is a single, threecenter two-electron bond directed to the middle of the metal triangle as shown.'4 A similar bonding scheme has been proposed
OOs
OS
...................___
for the linkage of the M(CO), groups to the Ni3 triangle in the pentanuclear cluster anions, [Ni,M2(C0),6]2-(M = Cr, Mo, W).Is It is also consistent with molecular orbital calculations for the squarepyramidal Cr(CO), fragment that indicate it has only one low-energy acceptor orbital of a i symmetry.I6 (9) Lauher, J . W. J. Am. Chem. SOC.1986, 108, 1521 and references therein. (10) For example: (a) Churchill, M. R.; Amoh, K. N.; Wasserman, H. J. Inorg. Chem. 1981, 20, 1609. (b) Harris, G. W.; Boeyens, J . C. A,; Coville, N. J. Organometallics 1985, 4 , 914. (c) Harris, G. W.; Boeyens, J. C. A,; Coville, N . J. J . Chem. Soc., Dalton Trans. 1985, 2277. (1 1) (a) Alex, R. F.; Pomeroy, R. K. Organometallics 1987, 6, 2437. (b) Mann, B. E.; Taylor, B. F. '3C N M R Data f o r Organometallic Compounds; Academic: New York, 1981; references therein. (12) We have chosen to label the unique carbonyl of the Cr(CO)5 an axial carbonyl even though it lies in the equatorial plane of the cluster. (13) Davis, H . B.; Pomeroy, R. K . , unpublished results. (14) Adapted from Porterfield's text.2 (15) Ruff, J. K.; White, R. P.; Dahl, L. F. J . Am. Chem. SOC.1971, 93, 2159. (16) Elian, M.; Hoffmann, R. Inorg. Chem. 1975, 14, 1058.
J . Am. Chem. SOC.1988, 110, 4453-4454 Stone and co-workers have pointed out that the I3C N M R ( M = Cr, Mo, W) spectra of (OC)5M[Rh2(pCO),(05-C5Me5)2] are consistent with free- rotation of the dirhodium fragment about an axis through the metal atom M and perpendicular to the Rh-Rh vect0r.l' This is, of course, equivalent to considering the rotation as that of the M(CO), unit about the Rh2 moiety. That metal atoms and their associated ligands may freely rotate in cluster compounds may have general implications. For example, the observation that the carbonyls of each Os(CO), unit in OS,(CO),~(in solution at 100 "C) are equivalent but not equivalent to the carbonyls of the other chemically different Os(CO), unitsI8 may be rationalized in this way. When the temperature of the solution of 1 is raised above -122 "C there is immediate collapse of some of the N M R signals of A (but not B). The pattern of the coalescence of these signals is consistent with a partial equatorial merry-go-round C O exchange.19 Above -20 "C all the signals assigned to B collapse. This is consistent with terminal-bridge CO exchange in those two carbonyl-containing planes that are perpendicular to the CrOs2 plane and do not contain a phosphine ligand. The latter exchange which also exists in solution was observed in OS,(CO),,[P(OM~)~], as isomers analogous to A and B.Iia The exchange processes in 1 will be discussed in detail in a future publication.
Acknowledgment. We thank the Natural Sciences and Engineering Research Council of Canada and Simon Fraser University for financial support. Supplementary Material Available: Tables of atomic coordinates, temperature factors, and bond lengths and angles for 1 (4 pages). Ordering information is given on any current masthead page. (17) Barr, R. D.; Green, M.; Marsden, K.; Stone, F. G. A.; Woodward, P. J . Chem. SOC.,Dalton Trans. 1983, 507. See, also: Barr, R. D.; Green, M.; Howard, J . A. K.; Marder, T. B.; Stone, F. G. A. J . Chem. Soc., Chem. Commun. 1983, 759. (18) Eady, C. R.; Jackson, W. G.; Johnson, B. F. G.; Lewis, J.; Matheson, T. W. J . Chem. SOC.,Chem. Commun. 1975, 958. (19) (a) Mann, B. E. In Comprehensice Organometallic Chemistry; Wilkinson, G., Stone, F G. A.. Abel, E. W., Eds.; Pergamon: Oxford, 1982: Vol. 3, p 89. (b) Deeming, A. J. Ado. Organomet. Chem. 1986, 26, 1.
The Nontetrahedral Structure and Fluxional Character of SiLi,. A Violation of Both van't Hoff and Electrostatic Bonding Principlest%' Paul von Ragu6 Schleyer* and Alan E. Reed Institut fur Organische Chemie der Uniuersitat Erlangen-Nurnberg 8520 Erlangen, Federal Republic of Germany Received September 8.1987 Although SiLi4 is comprised of only two main group elements, its structure is unprecedented. Simple eight valence electron AX, molecules not only are expected to prefer tetrahedral geometries but also to possess configurational stability.2 If the A-X bonds are covalent, sp3 hybridization is strongly favored. If the A-X bonds are ionic, e.g., as in A4-(Xf)4, an electrostatic point charge model also dictates a tetrahedral geometry., The interactions 'This paper is dedicated to Professor Kurt Mislow on the occasion of his 65th birthday. ( I ) Presented at the World Association of Theoretical Organic Chemistry (WATOC) Congress, Budapest, Hungary, August 1987. ( 2 ) For discussions and leading references, see: (a) Pauling, L. The Nature o f t h e Chemical Bond Cornell: 1st ed.; 1938; 2nd ed.; 1948. (b) Gimarc, B. M. Molecular Strucrure and Bonding, Academic Press: New York, 1979; pp 50f, 59f. (c) Albright, T. A,; Burdett, J . K.; Whangbo, M. H . Orbital Interactions in Chemistry; Wiley: New York, 1985; pp 148f, 295f. (d) Gillespie, R . J.; Nyholm, R. S., Q.Reo. Chem. SOC.1957, 11, 339. (3) See: (a) Bartell, L. S.; Barshad, Y . Z. J . A m . Chem. SOC.1984, 106, 7700. (b) Bartell, L. S . Croar. Chim. Acta 1984, 57, 927. (c) Sachs. L. J. J . Chem. Ed. 1986,63, 288 and references cited. (d) For references to Bent, H. A.'s "tangent sphere model", see: Schultz, E. 1. Ibid. 1986, 63, 961.
0002-7863/88/ 1510-4453$01.50/0
4453
Scheme I. Optimized HF/3-21G(*) Geometries of SiLi., Species" +o.ss
L
+0.74
:
1
L .
I
1
835
177.9
+0.44
5
)84
-2.36
1
i
2 505 2 429 'I L
1
*0.74
c_ o&i +0.7S
il Ll
-'.e45 -
I I
2.398
,420
--,
/'
L ' Z 0 5
I
*0.74
--
51'4h[2) "Number of imaginary frequencies a r e in parenthesis. T h e natural atomic charges a t HF/6-31G* a r e also given. Table I. Relative Energies of SiLi, Isomers (kcal/mol) 1, 2, 3, 4, 5, level G, Cd, GLinv Td D4h 3-21G//3-21G 0.0 3.8 1.5 2.2" 7.2 3-21G(*)//3-21G(*). 0.0 3.7 2.1 3.7" 7.3 6-31G*//3-21G(*) 0.0 3.1 1.8 3.6 8.3 MP2/6-31G*//3-21G(*) 0.0 3.3 3.3 6.6 11.4 3.4 ZPE 3.5 (3.6)' 3.4 3.1 (2.8)' 2 9 (2.9)' MP2/6-31GL ZPEb 0.0 3.2 2.9 6.1 11.3 "Structures optimized with Dld or C,, (regular) symmetries deviate only slightly in geometry and have essentially the same energy as the Td forms. b Z P E energies scaled by 0.9 (see ref 7). ?ZPE's at 3-21G(*)
+
among the hydrogens in methane are known to be repulsive, as is generally the case among ligands in AX, systems., Through ab initio calculations, we have been discovering molecules with rule-breaking structure^.^-^ While a number of these have been found to prefer anti van't HoffS geometries, none of these are as simple as SiLi4.8 (4) This is shown, e.g., by population analyses of various types. See ref 13 and 15. (5) Schleyer, P. v. R. Pure Appl. Chem. 1983, 55, 355; 1984, 56, 151. (6) (a) Krogh-Jespersen, K.; Cremer, D.; Poppinger, D.; Pople, J. A.; Schleyer, P. v. R.; Chandrasekhar, J. J. Am. Chem. SOC.1979, 101, 4843. (b) Schleyer, P. v. R.; Clark, T. J . Chem. SOC.,Chem. Commun. 1987, 1371. (7) Hehre, W. J.; Radom, L.; Schleyer, P. v. R.; Pople, J . A. A b Initio Molecular Orbital Theory; Wiley: New York, 1986. (8) SiLi, has been synthesized by the gas-phase reaction of Li atoms with SiCI4 (Morrison, J. A,; Lagow, R. J. Inorg. Chem. 1977, 16, 2972), but there has been no structural characterization of either the solid or the gas-phase material. Numerous other Si/Li stoichiometries are known experimentally see Wen et al., (Wen, C. J.; Huggins, R. A. J . Solid State Chem. 1981, 37, 271) and Dergochev et al. (Dergochev, Yu. M.; Elizarova, T. A,; Grechanaya, N. A. Russ. J . Inorg. Chem. (Engl. Trans.) 1982, 27, 1383) for references. For the crystal structure of Si7Lii2and discussions, see: von Schnering, H . G.; Nesper, R.; Curda, J.; Tebbe, K.-F. Angew. Chem., Int. E d . Engl. 1980, 19, 1033; Angew. Chem. 1980, 92, 1070. Liebman, J. F.; Vinant, J. S. Angew. Chem. Int. Ed. Engl. 1982, 21, 632; Angew. Chem. 1983, 94, 649. Both SiLi and Si2Li2have been studied in the gas phase (Ihle, H . R.; Wu, C. H.; Miletic, M.; Zmbov, K. F. Adu. Mass. Spectrosc. 1978, 7A, 670).
@ 1988 American Chemical Society
